1. Field of the Invention
The present invention relates to a power source device for an X-ray system, particularly, to a device capable of suppressing the current leakage to the casing of the device.
2. Description of the Related Art
A power source device for an X-ray system comprises in general a rectifying/smoothing circuit for converting an AC voltage to a rectified smooth voltage and a high voltage circuit for boosting the rectified smooth voltage to a high voltage for application to an X-ray tube. These rectifying/smoothing circuit and high voltage circuit are separately assembled within metal chassis, and these chassis are housed in a metal casing so as to form a power source device.
The chassis itself is electrically connected in general to the casing. The ground potential point of the rectifying/smoothing circuit is connected to the ground potential point of the high voltage circuit and to the ground terminal of the casing via a ground cable. The ground terminal is connected to the casing and to the ground terminal connected to the ground potential point of an external panel board via the ground cable.
A medical instrument such as an X-ray device is brought into contact with a human body directly or indirectly, leading to requirement of a complete guarantee of safety for protecting the patient, attendant and operator from electrical shocks. The medical instrument, e.g., X-ray device, is designed under the safety standard set for the medical instrument. The current leakage to the casing is specified in the safety standard. It is specified that a current meter should be connected between the ground terminal of the casing and the casing and that the current flowing through the current meter should be held below a certain level.
In the conventional X-ray device, the current leakage to the casing can be controlled to meet the safety standard because of the measure for connection to the ground potential point described above. In an X-ray device employing a power source circuit of a high frequency inverter system, however, the current leakage to the casing is several times to tens of times as large as in the conventional X-ray device, making it difficult to meet the safety standard without fail.